Abstract: In order to understand the widening process of dam breach in different slope sections of trench bed,seven sets of flume tests were carried out with the gradient of 7°~13°and the interval of 1°. Seven groups of experimental data were compared and analyzed to evaluate the influence of different ditch bed slopes on the process of dam breach widening. The following results and conclusions are obtained. (1)The process of breach widening of dam with overtopping failure is very similar at different slope sections. According to the characteristics of breach,the widening process can be divided into three stages: break through,mutation and formation of stable slope. (2)In the sudden change stage,the slope can lose stability many times along the x-axis direction. The top of the breach is in the shape of "S" on the downstream slope,in the shape of "U" on the dam crest and in the shape of "arc" on the upstream slope. (3)Different slope conditions can affect the outburst characteristics in the abrupt stage. With the increase of the slope of the gully bed,the scale of the single slope instability increases first and then decreases,and the number of the slope instability decreases first and then increases. (4)The stability of the breach slope mainly depends on the width of the side erosion and depth of the vertical erosion of the breach,which has a negative correlation with the difference between the width of the top and bottom side erosion of the breach,and a positive correlation with the depth of the vertical erosion of the breach. (5)The discharge of dam with different slopes has the same change trend with the extension of failure time. However,the peak discharge and the arrival time of the peak discharge are different at different slopes of the channel bed. With the increase of the slope of the channel bed,the peak discharge gradually decreases,and the arrival time of the peak discharge is first advanced and then postponed.